Side group mobility

Molecular Motion in amorphous atactic polystyrene (PS) is more complicated and a number of relaxation processes, a through 5 have been detected by various techniques as reviewed recently by Sillescu74). Of course, motions above and below the glass transition temperature Tg have to be treated separately, as well as chain and side group mobility, respectively. Motion well above Tg as well as phenyl motion in the glassy state, involving rapid 180° jumps around their axes to the backbone has been discussed in detail in Ref.17). Here we will concentrate on chain mobility in the vicinity of the glass transition. 

In some special cases, however, both the polymerization and the side group reorientation are single phase processes. They are of special interest for understanding the dynamics and side group mobility in the solid-state polymerization of diacetylenes. 

Although side-group mobility is obviously needed for efficient bonding, the majority of macromers are synthesized with side groups that have short spacers and are... 

Structural phase transitions accompanying solid state polymerization influence the behaviour of r(0 Thus they can not be observed but additional hints concerning the type of structural changes can be obtained. For example, a structural phase transition for DNP (Tab. 9.2) occurs at a polymer content above 95 % resulting in the loss of order perpendicular to the polymer chains [81], The accompanying increase of the side-group mobility results in a distinet increase of the electric permittivity [75]. Even more dramatic changes of r were observed at the transition to a fibrillar structure in polar crystals of DNP/MNP (Tab. 9.2) [74, 75]. 

Figures 11.8 through 11.10 contain the respective results for the backbone and side group mobilities.

The fluidity is one of the most vital properties of biological membranes. It relates to many functions involved in biological system, and effective biomembrane mimetic chemistry depends on the combination of both stability and mobility of the model membranes. However, in the polymerized vesicles the polymer chain interferes with the motion of the side groups and usually causes a decrease or even the loss of the fluid phases inside the polymerized vesicle (72,13). 

This ensures the necessary ordering of reacting side groups for an elementary act to take place although the copolymer macromolecules exhibit a low mobility 109). 

Side-chain mobility is of particular interest because groups responsible for protein function are in many cases located in side chains rather than in the backbone. Gaining an insight into side-chain dynamics, therefore, could be necessary for understanding the relationship between protein dynamics and function. In contrast to protein backbone dy-... 

The stronger deviations from Gaussian behaviour for PVE, a polymer with large side groups (see Table 1.1), could be caused by the different mobility of the hydrogens linked to the main chain carbons and those in the side groups. This hypothesis could be confirmed by the MD simulations. Distinguishing the... 

Thus, LC polymers of the type considered exhibit intramolecular order of mesomorphic type, mesogenic side groups forming a mobile LC structure. 

This was qualitatively shown in investigations of conformational behaviour and intramolecular mobility (IMM) of cholesterol-containing polymers in dilute solutions as of a function of solvent quality 134-136,185-l88) and temperature. Polarization luminescence provides one of the most fruitful methods for the evaluation of IMM l75,176). The method permits to get direct information about rotational mobility of the macromolecule as a whole, as well as about the mobility of the main chains and side branches. This is achieved via the attachment to macromolecules of so called luminescent markers (LM) — anthracylacyloxymethane groups in the case reported. Below are shown the chain fragments with LM which give information on the mobility of main chains (LM-1) and of side groups (LM-2) ... 

The variation of the temperature interval of structure formation is also accounted for by the effect of side chain mobility on mesophase nucleation. The solutions of cholesterol-containing polymers with longer spacer groups have to be cooled further for mesophase nuclei to be formed. For instance, in a series of PChMO-n polymers the interval of structure formation is for PChMO-14 — 308-313 K, for PChMO-lO — 323-333 K and for PChMO-5 the internal structure is formed at even higher temperatures 187). 

In order to assess the orientational stability of the poled state, the temperature dependence of the dipole mobility of the side groups was examined through dielectric relaxation measurements. (13) No low temperature relaxation below Tg was observed in the frequency range studied (100 Hz-100 kHz). In addition, the dielectric constant was approximately equal to the square of the refractive index, indicating that below T only electronic and no significant orientational contributions to the dielectric displacement are present. Thus, it was expected that a given orientational state of the ensemble would be stable at temperatures significantly below Tg. 

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